Process for manufacturing glass optical elements

ABSTRACT

Disclosed are processes for manufacturing glass optical elements by press molding a heated and softened glass material in preheated molds. In the process, the glass material is heated while it is floated by a gas blow and the heated and softened glass material is transferred to the preheated molds and then subjected to press molding. Alternatively, the process comprises: heating a glass material at a temperature at which the glass material has a viscosity of lower than 10 9  poises, preheating molds at a temperature at which the glass material has a viscosity of from 10 9  to 10 12  poises, subjecting the heated and softened glass material to initial press in the preheated molds for 3 to 60 seconds, starting to cool the vicinity of molding surfaces of the molds at a rate of 20° C./minute or higher upon starting of, or during, or after the initial press, and removing a molded glass article from the molds after the temperature of the vicinity of the molding surfaces of the molds becomes a temperature equal to or lower than a temperature at which the glass material has a viscosity of 10 12  poises.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for manufacturingglass optical elements such as glass lenses, which require no grindingand polishing after their press molding. In particular, the presentinvention relates to a process for manufacturing glass optical elements,which can improve production speed by markedly shortening the cycle timerequired for the press molding.

[0002] There have been known various processes for manufacturing glassoptical elements, which require no grinding and polishing after theirpress molding, by molding glass preforms, which are glass materials tobe further molded, in molds which ensure surface accuracy and surfaceroughness required for surfaces of molded glass articles.

[0003] For example, Japanese Patent Un-examined Publication (KOKAI,hereinafter referred to as “JP-A”) No. 64-72929 and Japanese PatentPublication (KOKOKU, hereinafter referred to as “JP-B”) No. 2-16251disclose processes where molds and glass preforms are heated together.In these methods, a glass preform is inserted into a mold assemblycomprising an upper mold, a lower mold and a guide mold which guides theupper mold and the lower mold, and the preform is heated together withthe mold assembly to a temperature where the preform is softenedsufficiently and then the preform is subjected to press molding. Then,they are cooled at such a cooling rate that surface accuracy of theglass article after molding is not deteriorated to a temperature aroundthe glass transition temperature, or allowed to cool to room temperaturewith a certain period of time, and the molded glass article is removedfrom the mold assembly.

[0004] JP-A-62-113730 and JP-B-63-46010 disclose processes where apreliminarily softened glass preform is inserted into a separatelyheated mold assembly. In these methods, a glass preform placed on aring-like member is softened by heating it together with the ring-likemember, inserted into a mold assembly with the ring-like member andpress molded between an upper mold and a lower mold which penetrates thering-like member and lifts up the softened preform. Alternatively, thering-like member acts as a guide mold guiding the upper mold and thelower mold to perform the press molding. JP-A-61-251529, JP-A-61-286232,JP-A-62-27334 and JP-A-63-45134 also disclose processes for moldingglass optical elements where a preliminarily softened glass preform isinserted into a separately heated mold assembly. However, theseprocesses have drawbacks that they occasionally cannot mold a desiredshape when relatively large deformation of the glass material isrequired, and that they are likely to generate sink marks and distortionand thus difficult to obtain sufficient surface accuracy.

[0005] JP-A-62-27334 discloses a process where a glass preform isinserted into a mold assembly by using a ring-like member and molded, aswell as temperature conditions for prolonging the lifetime of molds forsuch a process. In this method, the mold temperature is maintainedwithin a temperature range of from a temperature just below the glasstransition point to a temperature lower than the glass transition pointby 200° C., and a glass preform, which has been preliminarily heated tosuch a temperature that the preform had a viscosity ranging from 10⁶ to10⁸ poises, is inserted into the mold assembly and press molded.

[0006] In the above-mentioned processes where a preform is heated,molded and cooled with molds while the preform is maintained in a moldassembly, the temperatures of the glass and the molds are approximatelythe same throughout the molding process and hence there would be notemperature difference between the surface and the inside of the glass.Therefore, sink marks are prevented and thereby high surface accuracy isprovided. However, since it requires a temperature elevating periodbefore the pressing and a cooling period after the pressing and beforethe ejection, it has a drawback of extremely long cycle time requiredfor the whole process. In addition, since the glass is contacted withmold surfaces for a long period of time during the heating and thepressing, it has also a drawback that the glass is likely to react withthe mold surfaces and thereby the lifetime of the molds is shortened.

[0007] On the other hand, in the process where a glass preform which ispreliminarily heated to have a higher temperature (low viscosity) thanmolds is inserted into the molds by using a ring-like member and pressmolded, press time may be very short. In addition, since the moldtemperature may be relatively low and release of a molded glass frommolds is possible after a relatively short period of time to allow themolded glass to cool after the pressing, the cycle time can be markedlyshortened. However, if the preform is inserted into the molds at a lowtemperature (within a temperature range of from a temperature just belowthe glass transition point to a temperature lower than the glasstransition point by 200° C. ) to prolong the lifetime of the molds, thetemperature of the glass surface is rapidly lowered and the glass iscooled and solidified before it is press molded to a desired thickness.Therefore, it has drawbacks that it cannot stably provide moldedarticles, especially glass molded articles with a small edge thickness(about 1.0 to 1.3 mm) such as biconvex lenses and meniscus lenses, andthat it shows insufficient surface accuracy.

[0008] To solve the above-described problems, it has been proposed touse a glass preform showing a further lower viscosity under similartemperature conditions of molds. However, as the viscosity becomeslower, the softened preform on the ring-like member becomes more likelyto sag at the opening of the ring member (deformed and hanged down). Forexample, though it depends on the shape of the preform, when theviscosity is 10⁷ poises or lower, the preform is very likely to sag.Therefore, to prevent deformed preform from dropping down from thering-like member, it is necessary to use a glass preform having an outerdiameter quite larger than the inner diameter of the preform supportingportion of the ring-like member.

[0009] As a result of it, press molded lenses have a quite larger outerdiameter than desired and hence it is necessary to cut off a largesurplus in a post-processing so that they have a desired outer diameter.Further, in this method using a ring-like member, since molding flash isproduced due to the use of a preform larger than the final product andthe generation of surplus and, since a low mold temperature is used, itis very difficult to produce biconvex lenses, meniscus lenses and thelike with a small edge thickness.

[0010] Therefore, one of the objects of the present invention is toprovide a process for manufacturing glass optical elements by pressmolding a heated and softened glass material such as a glass preform inpreheated molds, wherein the glass material is easily held during itsheating and softening even if a glass material such as a glass preformof which viscosity is decreased when it is softened and hence which islikely to deform is used and thus a glass optical element can beproduced.

[0011] A further object of the present invention is to provide a processcapable of satisfactorily manufacturing glass optical elements bytransferring a heated and softened glass preform and the like, which isprone to be deformed, to molds without unduly deforming it.

[0012] A further object of the present invention is to provide a processfor manufacturing glass optical elements, which uses a glass materialsuch as a glass preform which enables to provide a molded glass with asize approximately the same with an effective outer diameter desired fora purpose glass optical element and therefore can minimize an edgingvolume for centering in a post-processing.

[0013] A further object of the present invention is to provide a processfor manufacturing glass molded articles of which cycle time required forpress molding is remarkably shortened and which can provide glass moldedarticles with no surface defects and with high surface accuracy.

[0014] An additional object of the present invention is to provide aprocess capable of easily manufacturing biconvex lenses, meniscus lensesand the like with a small edge thickness.

[0015] A still further object of the present invention is to provide aprocess capable of transferring a heated and softened glass gob, whichis prone to be deformed, to molds to satisfactorily manufacture glassoptical elements.

[0016] One of the objects of the present invention is to provide aprocess for manufacturing glass optical elements by press molding aheated and softened glass material such as a glass preform in apreheated molds, which can remarkably shorten the cycle time requiredfor the press molding, stably provide lenses and the like even thoughthey must have a small edge thickness and show good surface accuracy.

[0017] A further object of the present invention is to provide a processfor manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy.

[0018] A further object of the present invention is to provide a processcapable of manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy and a center thickness withinan allowance.

SUMMARY OF THE INVENTION

[0019] The present invention provides, as a first aspect of theinvention, a process for manufacturing glass optical elements by pressmolding a heated and softened glass material in preheated molds, whereinthe glass material is heated while it is floated by a gas blow and theheated and softened glass material is transferred to the preheated moldsand then subjected to press molding.

[0020] In one embodiment of the above-described process, the heated andsoftened glass material is transferred to the preheated molds bydropping the material.

[0021] In another embodiment of the above-described process, a heatedand softened glass material is transferred to the preheated molds byholding the glass material by suction or placing it on a ring-likemember having an inner diameter smaller than the outer diameter of theglass material and subjected to press molding.

[0022] In another embodiment of the above-described process, a heatedand softened glass material is transferred to the preheated molds bysplitting a floating means used for heating the glass material into twoor more pieces and removing the pieces to drop the glass material andthe glass material is subjected to press molding.

[0023] The present invention further provides, as a second aspect of theinvention, a process for manufacturing glass optical elements by pressmolding a heated and softened glass material in preheated molds, whichcomprises:

[0024] heating a glass material at a temperature at which the glassmaterial has a viscosity of lower than 10⁹ poises,

[0025] preheating molds at a temperature at which the glass material hasa viscosity of from 10⁹ to 10¹² poises,

[0026] subjecting the heated and softened glass material to initialpress in the preheated molds for 3 to 60 seconds,

[0027] starting to cool the vicinity of molding surfaces of the molds ata rate of 20° C./minute or higher upon starting of, or during, or afterthe initial press, and

[0028] removing a molded glass article from the molds after thetemperature of the vicinity of the molding surfaces of the molds becomesa temperature equal to or lower than a temperature at which the glassmaterial has a viscosity of 10¹² poises.

[0029] In one embodiment of the second aspect of the present inventiondescribed above, the molding surfaces of the molds have an amorphousand/or crystalline carbon mono-component or mixture layer of graphitestructure and/or diamond structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is an explanatory schematic view of press molding in a moldassembly used in the present invention.

[0031]FIG. 2 is an explanatory schematic view of the method forsoftening a floating glass preform above a floating means andtransferring the preform according to the present invention.

[0032]FIG. 3 is an explanatory schematic view of the method forsoftening a floating glass material above a floating means according tothe present invention.

[0033]FIG. 4 is an explanatory schematic view of the method forsoftening a floating glass preform above a floating means according tothe present invention.

[0034]FIG. 5 is an explanatory schematic view of the method forsoftening a floating glass preform above a floating means according tothe present invention.

[0035]FIG. 6 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0036]FIG. 7 is an explanatory schematic view of the method fortransferring a glass preform softened above a floating means to molds bysucking according to the present invention.

[0037]FIG. 8 is an explanatory schematic view of the method fortransferring a glass preform softened above a floating means to themolds by sucking according to the present invention.

[0038]FIG. 9 is an explanatory schematic view of the press molding in amold assembly used in the present invention.

[0039]FIG. 10 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0040]FIG. 11 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0041]FIG. 12 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0042]FIG. 13 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0043]FIG. 14 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0044]FIG. 15 is an explanatory schematic view of the method fortransferring a softened glass preform to molds according to the presentinvention.

[0045]FIG. 16 is an explanatory schematic view of the press molding in amold assembly used in the present invention.

[0046]FIG. 17 is an explanatory schematic view of a lower mold of a moldassembly used in the Examples.

[0047]FIG. 18 is an explanatory schematic view of press molding in amold assembly used in the Examples.

[0048]FIG. 19 is an explanatory schematic view of press molding in amold assembly used in the Examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] First Aspect of the Invention

[0050] The process according to the first aspect of the presentinvention is a process for manufacturing glass optical elements by pressmolding a heated and softened glass material to be molded in preheatedmolds.

[0051] Types, shapes and the like of the glass materials used for thepresent invention may be conventional ones. However, the glass materialsused for the present invention are preferably utilized at a relativelylow viscosity. For example, heated and softened glass materialspreferably has a viscosity of from 10^(5.5) to 10^(9.0) poises. Theglass materials may be in the form of, for example, a glass preform orglass gob. Glass preform is a term to refer to a molded article having adesired shape to be used as a precursor for manufacturing glass opticalelements. The glass preforms may be those obtained by cold forming orhot forming of molten glass and may be such preforms further subjectedto mirror polishing and the like. Further, the preforms may have roughsurfaces, rather than mirror surfaces, and, for example, may be groundarticles ground with #800 diamond.

[0052] The shape of the glass preforms is decided considering sizes,volumes of products, i.e., glass optical elements, their volume changesupon molding and the like. Further, in order to prevent formation of gastraps upon molding, it is preferred that glass preforms have such ashape that centers of molds initially contact with surfaces of thepreforms to be molded. For example, glass preforms may be spheres, orhave marble-like, disc-like shapes, or shapes having spherical surfacesand the like.

[0053] Glass gobs are glass pieces obtained by splitting molten glassinto a desired volume and they usually have irregular chill marks.Examples of the above-described glass preforms are obtained by moldingthese glass gobs into a desired shape. Glass gobs are softened byheating while they are floated, and they may be heated so that they havea glass viscosity of 10⁵ poises or lower to eliminate wrinkles (chillmarks) on their surfaces.

[0054] Volumes of glass preforms or gobs may be slightly larger thanthose of final products and, in such a case, final outer diameters canbe obtained by subjecting the molded articles to edging inpost-processing.

[0055] For the present invention, mold structure may have a structurewhere pressure is applied to molded articles (optical elements) duringcooling after molding, or a structure where pressure can be reducedafter initial press. Further, they may have a structure where pressureis applied by weight of upper molds after the initial press. Molds canbe heated by resistance heaters, high-frequency heaters, infrared lampheaters and the like. In particular, high-frequency heaters and infraredlamp heaters are preferred, since they can recover mold temperature in ashort period of time. Cooling of molds can be performed by electric cutcooling, cooling gas passing through inside of molds and the like.

[0056] The molds used for the present invention may be, for example, amold assembly 39 comprising an upper mold 35, a lower mold 34 and aguide mold 36 as shown in FIG. 1. However, molds are not limited to it.The molds may be those obtained by forming a silicon carbide layer on asilicon carbide sintered body by a CVD technique and forming thereon ani-carbon (diamond-like carbon) layer by an ion-plating technique. Alsoused are those composed of silicon, silicon nitride, tungsten carbide orcermets of aluminum oxide-base and cermets of titanium carbide-base andsuch materials of which surfaces are preferably further coated withdiamond, heat resistant metals, noble metal alloys, ceramics ofcarbides, nitrides, borides, oxides and the like. Those having carboncoatings such as i-carbon coatings are particularly preferred, becausethey show excellent releasability.

[0057] Conditions for press molding may be suitably selected dependingon temperatures (viscosities) of glass materials such as preforms andgobs and temperatures of molds and the like. Normally, molding isperformed by pressing at a pressure of from 30 to 300 kg/cm² for 3 to 60seconds, preferably 5 to 30 seconds. Temperature of glass materials,mold temperature and mold release temperature may also be optionallyselected.

[0058] The manufacturing process according to the first aspect of thepresent invention is characterized in that preheating of a glassmaterial is carried out by heating the glass material while it isfloated by a gas blow and the heated and softened glass material istransferred to the preheated molds.

[0059] In a viscosity range where the glass materials are deformed bytheir own weight, it is not easy to prevent adhesion between the glassmaterials and the means for supporting the glass materials upon heating.According to the present invention, the glass materials are floated by agas blow, for example, by blowing gas from inside of the supportingmeans. As a result, gas layers are formed on both surfaces of the meansand the glass materials and it is made possible to heat and soften theglass materials while obviating any reaction between the supportingmeans and the glass materials. Further, when the glass material is aglass preform, the glass preform may be heated and softened while theshape of the preform is substantially maintained. When the glassmaterial is a glass gob, it is possible to deform the gob to obtain itsappropriate shape and eliminate its surface defects by heating andsoftening it while it is floated by a gas blow even if the glass gob hashad an irregular shape and surface defects such as wrinkles.

[0060] Gas for the gas blow used for floating the glass materials in thepresent invention is not particularly limited. However, it is preferablya non-oxidative gas such as nitrogen, since the heated glass materialshould not react with the supporting means and deterioration of thesupporting means by oxidation should be prevented. Reducing gas such ashydrogen gas may be added to the gas.

[0061] Flow rate of the gas may be suitably selected depending on shapesof an outlet for the gas blow, shapes and weights of the glass materialsand-the like. Normally, a flow rate ranging from 0.005 to 20liters/minute is suitable for floating the glass materials. When theflow rate is lower than 0.005 liters/minute, it may sometimes beimpossible to satisfactorily float the glass materials. When the flowrate exceeds 20 liters/minute, the glass material above the supportingmeans is unduly swayed and, when the glass material is a glass preform,it may be deformed upon heating even though it has a weight of not lessthan 2000 mg.

[0062] Conditions for heating and softening the glass materials may besuitably selected depending on types of the glass materials and the likeand adjusted so that softened glass materials have a desired viscosity.

[0063] The glass materials can be floated by a gas blow which is blownoff upward from an upper opening having an opening diameter smaller thana diameter of the glass materials. As shown in FIG. 2, an upper opening11 of a floating means 10 has a diameter smaller than that of a glassmaterial 1, and the glass material 1 is floated and maintained above theupper opening 11 by a gas blow blowing off upward from the bottom 12 ofthe upper opening 11 of the floating means 10 so that the material isnot contacted with the floating means 10. The floating means 10 may be,as shown in FIG. 3, composed of separable two portions 10 a and 10 b.The glass material 1 is heated by surrounding heaters for softeningglass 14.

[0064] The glass materials may be, whether they may be a glass preformor gob, floated by a gas blow as shown in FIG. 3.

[0065] The glass materials may also be floated by a gas blow blowing offfrom a spherically hollowed surface of a porous material having acurvature similar to that of the shape of glass material or a flatsurface of a porous material. In particular, when the glass material isa glass preform, it is effective since it makes it very easy to maintainthe shape of the preform. When the glass material is a glass gob, it isalso possible to easily eliminate surface defects of the glass gob byheating it while it is floated by a gas blow from a porous surface.

[0066] As shown in FIG. 4, the glass material 1 is maintained in afloating state by a gas blow blowing off from the porous surface 18above the floating means 17, which is supported by a floating meanssupport 19 and has a spherical porous surface 18 of which curvature issimilar to that of the glass material 1. The floating means support 19and the floating means 17 may have, like in FIG. 3, a split structure.The glass material 1 is heated by the surrounding heaters for softeningglass 14.

[0067] The heating of the glass materials includes heating the materialsof an ambient temperature to a desired temperature, or heating thematerial of a somewhat elevated temperature to a desired temperature. Inaddition, a glass material already heated to a desired temperature mayalso be used. For example, when the glass material is a glass gob, aglass gob made of molten glass may be used without cooling it.

[0068] Therefore, the present invention encompasses a process formanufacturing glass optical elements by press molding a heated andsoftened glass material in preheated molds, wherein the glass materialis a softened glass gob which is obtained by taking a portion of moltenglass and the glass gob is floated by a gas blow to eliminate surfacedefects of the glass gob, then transferred to the preheated molds andpress molded.

[0069] To obtain a glass gob by taking a portion from molten glass, anyconventional method can be used. For example, a softened glass gob witha desired volume can be obtained by cutting off a glass piece frommolten glass melted at a desired temperature. Elimination of surfacedefects of glass gobs can be efficiently performed by floating the glassgobs having a viscosity of not more than 10⁵ poises by a gas blow.

[0070] When the glass material is a glass preform, it may first beheated to a temperature lower than its glass transition temperature by30° C. or more and then further heated to a desired temperature while itis floated by a gas blow. Such a process is shown in FIG. 5. As shown inFIG. 5, the glass material 1 is heated on a means for supporting glassmaterial 20 to a temperature lower than the glass transition temperatureby 30° C. or more. Then, the heated glass material 1 is transferred tosuch a floating means as shown in FIG. 2 or 3 by means of an appropriatetransfer means. In FIG. 5, exemplified is transfer of glass material 1to a floating means 10 by means of a movable suction holding means 15having a lower opening. For the transfer of the heated glass material 1,any means other than the above-described suction holding means, such asa ring-like member on which a glass material is placed may also be used.

[0071] In one embodiment, a heated and softened preform may betransferred to preheated molds by holding the preform by suction. Forexample, such transfer may be performed by the movable suction holdingmeans 15 having a lower opening 16 shown in FIG. 2. The lower opening 16is connected to a means for internally sucking such as reduced pressurepumps and vacuum pumps and the lower opening 16 is capable of holding aglass preform by suction. A glass preform 1 heated and softened abovethe floating means 10 is held at the lower opening 16 of the movableholding means 15 by suction and transferred to a position over themolding surface 40 of the lower mold 34 as shown in FIG. 6. Then, thesoftened preform 1 is press molded by the molding surface 40 of thelower mold 34 and the molding surface 41 of the upper mold 35 as shownin FIG. 1 to give an glass optical element 2.

[0072] The heated and softened preform may also be held by suction bysucking from suction holes provided in the vicinity of the moldingsurface of the upper mold. For example, it may be held by sucking fromthe suction holes 45 provided on the guide mold 36 disposed in thevicinity of the molding surface 41 of the upper mold 35 shown in FIG. 7.As shown in FIG. 7, the softened preform 1 above the floating means 10is transferred to a position near the lower opening of the guide mold 36provided together with the upper mold 35, and then, as shown in FIG. 8,the preform 1 is lifted and stuck to the molding surface 41 by suckingfrom the suction holes 45 of the guide mold 36. Then, the floating means10 is removed, a lower mold is transferred to a position under thesoftened preform or the softened preform held by suction at the vicinityof the molding surface of the upper mold is transferred to a positionover a molding surface of the lower mold, and the preform may be pressmolded by the molding surfaces of the upper mold and the lower mold(FIG. 9).

[0073] Transfer of a heated and softened preform to preheated molds mayalso be performed by placing the preform on a ring-like member having aninner diameter smaller than the outer diameter of the preform andholding by suction the member on which the preform is placed.

[0074] For example, as shown in FIG. 10, a ring-like member 23 having aninner diameter slightly larger than the outer diameter of the upperopening of the floating means 10 and smaller than the outer diameter ofthe preform 1 is placed so that the upper opening of the floating means10 is positioned within the ring of the ring-like member 23. After thepreform is softened to a desired viscosity, the preform heated andsoftened while floating above the floating means 10 is placed on thering-like member 23 and transferred. For the transfer of the ring-likemember 23, vacuum pad 24 capable of holding the ring-like member 23 bysuction is exemplified in FIG. 10. However, means for transferring thering-like member is not particularly limited.

[0075] Then, as shown in FIG. 11, the preform 1 is transferred to aposition over the molding surface 40 of the lower mold 34 on which thepreform 1 is to be placed, and the suction of vacuum pad 24 is stoppedto place the preform 1 on the molding surface 40. The preform 1 on themolding surface 40 is press molded between the upper and lower molds asshown in FIG. 1.

[0076] In another embodiment according to the first aspect of thepresent invention, the transfer of the heated and softened glassmaterial is performed by dropping the softened glass material. Theheated and softened glass material may be dropped, for example, bysplitting a floating means into two or more pieces and removed thepieces to make an opening under the material. For example, as shown inFIG. 12, the glass material 1 is softened by heating above the floatingmeans 10 and then the glass material 1 is dropped since the floatingmeans 10 is horizontally separated into two parts, 10 a and 10 b, andmoved to opposite directions (right and left in the figures) as shown inFIG. 13. The lower mold 34 is provided as a receiver of the droppedglass material 1 and thus the glass material 1 is transferred onto themolding surface 40 of the lower mold 34 in a moment.

[0077] Further, in the above-described embodiment, a guide means may beutilized to drop and transfer the heated and softened glass materialonto the center position of the molding surface without any deviation.For example, as shown in FIGS. 12 and 13, the cylindrical guide means 50having an inner diameter capable of providing an appropriate clearanceagainst the maximum outer diameter of the glass material 1, which iscomposed of separable portions 50 a and 50 b, is provided above thefloating means 10, and thus the glass material can be dropped onto thecenter of the mold. Structure and the like of the guide means would notbe particularly limited, so long as it can prevent deviation of theglass material upon split and removal of the floating means. Forexample, the guide means may be composed of, not a cylinder, but aplurality of pipes arranged as a grille, or two or more facing panels.The guide means may have a structure which can be removed as two or moreportions. Further, the guide means may be provided under the floatingmeans.

[0078] Structure for separating and removing the floating means used forheating the glass material is not particularly limited. For example,when the floating means is moved horizontally as described above, thefloating means may be separated into three or four portions and therespective portions may be removed along three directions (adjacentdirections are different by 120°) or four directions (adjacentdirections are different by 90°) respectively to drop the glassmaterial.

[0079] Further, the floating means may also be composed of floatingmeans portions 17 a and 17 b, which have pivot shafts 18 a and 18 brespectively, as shown in FIG. 14. The floating means portions 17 a and17 b can move downward by pivoting around the shafts 18 a and 18 b and,as a result of such pivoting movements, the floating means can opendownward to drop the glass material 1. Further, as shown in FIG. 15, thefloating means may also be composed of floating means portions 19 a and19 b, which have pivot shafts 18 a and 18 b respectively. The floatingmeans portions 19 a and 19 b can move downward by pivoting around theshafts 18 a and 18 b and, as a result of such pivoting movements, thefloating means can open downward to drop the glass material 1.

[0080] In the embodiment of the present invention described above, theheated and softened glass material can be transferred into the molds ina moment by dropping the glass material.

[0081] Though the above-described embodiment has been explained byreferring to softening and molding of glass preforms, glass opticalelements can be manufactured by heating, transferring and molding glassmaterials other than glass preforms, for example, glass gobs.

[0082] Second Aspect of the Invention

[0083] The process according to the second aspect of the presentinvention is a process for manufacturing glass optical elements by pressmolding heated and softened glass material in preheated molds, whichcomprises:

[0084] heating a glass material at a temperature at which the glassmaterial has a viscosity of lower than 10⁹ poises,

[0085] preheating molds at a temperature at which the glass material hasa viscosity of from 10⁹ to 10¹² poises,

[0086] subjecting the heated and softened glass material to initialpress in the preheated molds for 3 to 60 seconds,

[0087] cooling the vicinity of molding surfaces of the molds at a rateof 20° C./minute or more, and

[0088] removing a molded glass article from the molds after thetemperature of the vicinity of the molding surfaces of the mold becomesa temperature equal to or lower than a temperature at which the glassmaterial has a viscosity of 10¹² poises.

[0089] In one embodiment of the second aspect of the present inventiondescribed above, the molding surfaces of the molds have an amorphousand/or crystalline carbon mono-component or mixture layer of graphitestructure and/or diamond structure.

[0090] Types, shapes and the like of glass materials used in the processaccording to the second aspect of the present invention may be similarto those used for the process according to the first aspect of thepresent invention.

[0091] In this molding process of the present invention, the glassmaterial is softened by heating it to a temperature at which the glassmaterial has a viscosity of lower than 10⁹ poises. Because of theviscosity of the glass material lower than 10⁹, poises, the glassmaterial can be sufficiently deformed and molded in the molds preheatedto a temperature at which the glass material has a viscosity not lessthan 10⁹ poises. To carry out the molding with a relatively low moldtemperature, it is preferred that the glass material is softened byheating it to a temperature at which the glass material has a viscosityof from 10^(5.5) to 10^(7.6) poises.

[0092] The molds are preheated at a temperature at which the glassmaterial has a viscosity of from 10⁹ to 10¹² poises. At a temperaturelower than a temperature at which the glass material has a viscosity of10¹² poises, it is difficult to sufficiently extend the glass materialto obtain glass molded articles having a thin edge thickness, and it isalso difficult to obtain high surface accuracy. At a temperature ofmolds higher than a temperature at which the glass material has aviscosity of 10⁹ poises, molding cycle time is unduly prolonged and moldlifetime is shortened.

[0093] Conventional molds can be used for the present invention as theyare. However, those of which molding surfaces have an amorphous and/orcrystalline carbon mono-component or mixture layer of graphite structureand/or diamond structure are preferred. In the molds having such carbonlayers as described above, adhesion of glass would not occur even thoughthe mold temperature is higher than the glass transition point of theglass material.

[0094] The carbon layers described above can be formed by spatteringtechniques, plasma CVD techniques, CVD techniques, ion platingtechniques and the like. When the layers are formed by a spatteringtechnique, spattering is preferably carried out by using a substratetemperature of 250 to 600° C., RF power density of 5 to 15 W/cm², degreeof vacuum during spattering of 5×10⁻⁴ to 5×10⁻¹ torr as well as an inertgas such as Ar as spattering gas and graphite as a spattering target.

[0095] When the layers are formed by a microwave plasma CVD technique,they are preferably formed under conditions of a substrate temperatureof 650 to 1000° C., microwave power of 200 W to 1 kW, gas pressure of10⁻² to 600 torr by using methane and hydrogen gases as raw materialgases.

[0096] When the layers are formed by an ion plating technique, they arepreferably formed by using a substrate temperature of 200 to 450° C. andionizing benzene gas.

[0097] The carbon layers include those with and without C—H bonds.

[0098] In this press molding process of the present invention, theheated and softened glass material is subjected to initial press in thepreheated molds for 3 to 60 seconds. When the initial press is shorterthan 3 seconds, extension of the glass would be insufficient and henceglass optical elements of desired shapes cannot be obtained. On theother hand, though longer initial press can provide higher surfaceaccuracy, long initial press time makes it impossible to shorten cycletime and sometimes badly affects on mold lifetime, and therefore itshould be equal to or shorter than 60 seconds. Molding pressure may beappropriately selected considering temperatures of the glass materials,molds and the like, and it may normally be a pressure in a range of from30 to 300 kg/cm³.

[0099] After molding, the vicinity of the molding surfaces of the moldsis cooled at a rate equal to or more than 20° C./minute. The coolingrate may be smaller than 20° C./minute, but it only results in anunnecessarily long molding cycle time. Though it may vary depending onsizes and shapes of molded articles, it is preferred that the vicinityof the molding surfaces is cooled at a rate of from 20 to 180° C./minuteto obtain high surface accuracy.

[0100] After the initial press, secondary press is preferably carriedout at a constant pressure corresponding to 5 to 70% of the pressure ofthe initial press and the vicinity of the molding surfaces is cooledwhile maintaining the pressure, because this may provide good surfaceaccuracy without sink mark and surface distortion. More preferably, thesecondary press is carried out at a pressure corresponding to 20 to 50%of the pressure used for the initial press.

[0101] Further, to obtain final products with a center thickness withinthe allowance, it is preferred that the heated and softened glassmaterials are initially pressed so that it has a center thickness within a range of from a thickness smaller than that of final products by0.03 mm to a thickness larger than the same by 0.15 mm, and thensubjected to the secondary press. Since in the secondary press thepressure is rapidly reduced and the glass have a high viscosity, thecenter thickness may be changed only by about 0.001 to 0.12 mm and henceit is easy to obtain the center thickness within a range of theallowance ±0.03 mm.

[0102] Regarding the initial press and the secondary press describedabove, the initial press is preferably stopped by a means for stoppinginitial press so that the glass material has a desired center thickness,i.e., a thickness within a range of from a thickness smaller than thatof final products by 0.03 mm to a thickness larger than the same by 0.15mm, and the secondary press is preferably started before the initialpress is stopped or upon the stop of the initial press. Such anoperation results in a desired center thickness and good surfaceaccuracy because the initial press and the secondary press are carriedout with continuous pressurization. When the desired center thickness isobtained by, for example, an external stopper, and then the secondarypress is performed, it sometimes becomes difficult to obtain goodsurface accuracy because the press operation is interrupted for amoment. The initial press and the secondary press described above arepreferably carried out in a double cylinder structure. Such a doublecylinder structure will be explained in detail in the Exampleshereinafter.

[0103] The glass molded articles press molded and cooled as describedabove are released from the molds when the temperature of the vicinityof the molding surfaces becomes below a temperature at which the glassmaterial has a viscosity of 10¹² poises. Glass materials having aviscosity exceeding 10¹² poises do not show viscous flow in a shortperiod of time and may be considered substantially solidified.Therefore, deformation and the like of the glass molded articles afterthe release from molds are prevented and good surface accuracy can beobtained. It is particularly preferred that the glass molded articlesare released from the molds at a temperature at which the glass materialhas a viscosity of 10¹³ to 10^(14.5) poises.

[0104] The molds used in this process of the present invention are notparticularly limited except for the molding surfaces. Those means forheating and cooling the molds described for the first aspect of thepresent invention may also be used for this process.

[0105] The molds used for this process of the present invention may be,for example, a mold assembly 39 comprising an upper mold 35, a lowermold 34 and a guide mold 36 as shown in FIG. 16. However, molds are notlimited to it. The molds may be those composed of silicon carbide,silicon, silicon nitride, tungsten carbide or cermets of aluminumoxide-base and cermets of titanium carbide-base and such materialspreferably further coated with diamond, heat resistant metals, noblemetal alloys, ceramics of carbides, nitrides, borides, oxides and thelike. Particularly preferred are those obtained by forming a siliconcarbide layer on a silicon carbide sintered body by a CVD technique,processing it into a finished shape and forming thereon an amorphousand/or crystalline carbon mono-component or mixture layer of graphitestructure and/or diamond structure such as i-carbon layers by anion-plating technique or the like. In the molds having such carbonlayers as described above, adhesion of glass by fusion would not occureven if the molding is carried out at a relatively high moldingtemperature and molded articles are easily released from the molds at arelatively high temperature because of good mold release property.

[0106] In this process of the present invention, like the processaccording to the first aspect of the present invention, heating andsoftening of the glass materials can be performed while the materialsare floated by a gas blow and the heated and softened glass materialsare transferred to the preheated molds.

[0107] Type and flow rate of the gas for floating the glass materials byits blow may be similar to those described for the process according tothe first aspect of the present invention, and floating of the glassmaterials by a gas blow and transfer of the glass materials may also becarried out as described for the process according to the first aspectof the present invention by referring to FIGS. 2 to 15.

[0108] According to the present invention, in a process formanufacturing glass optical elements by press molding a heated andsoftened glass material in preheated molds, even if the glass materialis likely to be deformed when it is softened to a low viscosity, it canbe heated and softened while easily holding it.

[0109] According to the present invention, glass optical elements havinggood optical properties can be manufactured by transferring a heated andsoftened glass material which is likely to be deformed to molds withoutunduly deforming it.

[0110] According the the present invention, glass optical elements canbe manufactured by using a glass material which enables to provide amolded glass having a size approximately the same as the desired size ofa purpose glass optical element after molding so that an edging volumefor centering in post-processing may be minimized.

[0111] Further according to the present invention, glass opticalelements having few surface defects and high surface accuracy can bemanufactured while the cycle time required for the molding is markedlyshortened.

[0112] In addition, according to the present invention, even biconvexlenses, meniscus lenses and the like with a small edge thickness can beeasily manufactured.

[0113] According to the present invention, glass optical elements havinggood properties can be manufactured by transferring a heated andsoftened glass gob, which is prone to be deformed, to molds.

[0114] According to the present invention, it is possible to provide aprocess for manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy.

[0115] According to the present invention. it is possible to provide aprocess capable of manufacturing glass optical elements without sinkmarks and distortion and with high surface accuracy and a centerthickness within allowance.

[0116] That is, according to the present invention, glass opticalelements with few surface defects and high surface accuracy can bemanufactured with a markedly shortened cycle time required for the pressmolding when compared with that of conventional processes by heatingmolds and glass preforms together (5 to 20 minutes/cycle).

[0117] Further, the present invention provides a process capable ofmanufacturing glass optical elements while completely preventing glassadhesion to molding surfaces.

EXAMPLES

[0118] The present invention will be further explained by referring tothe following examples.

Example 1

[0119] Molds for Press Molding

[0120] Molds for press molding comprised, as shown in FIG. 17, a moldsubstrate which was obtained by grinding a substrate material of siliconcarbide (SiC) sintered body 31 into a shape of mold for press molding,forming a silicon carbide layer 32 on the molding surface portion by aCVD technique, grinding and polishing the surface to finish it as amirror surface corresponding to the shape of glass molded articles to beproduced. A layer of i-carbon (diamond-like carbon) 33 with a thicknessof 500 Å was further formed on the silicon carbide layer 32 of-the moldsubstrate by an ion plating technique to give a lower mold 34 having amolding surface 40 for manufacturing φ 18 mm biconvex glass lenses (φ 15mm after edging for centering).

[0121] An upper mold 35 shown in FIG. 1 was also obtained in a mannersimilar to that for obtaining the lower mold 34 described above. Theupper mold 35 and the lower mold 34 are disposed coaxially as shown inFIG. 1, and a mold assembly 39 was constituted by the upper mold 35 andthe lower mold 34 as well as a guide mold 36 for guiding them upon pressmolding.

[0122] The lower mold 34 and the upper mold 35 were heated by moldheaters 44, which were provided around the outside of cylindrical molds37 and controlled by a thermocouple 44 for measuring mold temperatureinserted into inside of the lower mold 34 from lower part of a moldsupport 38. Temperature of the cylindrical molds 37 was measured bythermocouples 43 for measuring cylindrical mold temperature insertedinto inside of the cylindrical molds 37.

[0123] Floating Means and Transfer Means

[0124] In a single closed chamber (not shown) including the mold heatingstructure described above, there were also provided a floating means anda transfer means shown in FIG. 2.

[0125] A glassy carbon floating means 10 (hereinafter referred to as “GCfloating means”) set on a floating means support 13 is disposed betweenglass softening heaters 14 for heating and softening a glass material(preform) 1. The glass material 1 was floated and held by a gas blow of98% N₂+2% H₂ gas at a flow rate of 100 ml/minute fed from inside of thefloating means support 13 to lower part of the GC floating means 10.

[0126] Further, outside the glass softening heaters 14, there was aglassy carbon vacuum pad 15 (hereinafter referred to as “GC vacuumpad”), which can move vertically and horizontally, and it was normallywaiting at a position over the GC floating means 10. Preheating andPress Processes The closed chamber (not shown) including the pressmolding structure and the glass heating structure described above wasevacuated to vacuum and 98% N₂+2% H₂ gas was introduced into the chamberto form an atmosphere of the gas in the chamber.

[0127] Then, the mold assembly was heated by the mold heaters 44 untilthe temperatures of the upper mold 35 and the lower mold 34 reached to576° C. measured by the thermocouples 43 for measuring mold temperatureso that they had a temperature around the deformation point of thepreform 1 composed of barium borosilicate optical glass (marble-shapedhot formed article having a surface-defect-free mirror surface, weight;1000 mg, transition point; 534° C., deformation point; 576° C.) andmaintained at the same temperature. Glass viscosity at the transitionpoint is 10^(13.4) poise and that at the deformation point is 10¹⁰⁻¹¹poise.

[0128] On the other hand, the glass preform 1 floating above the GCfloating means 10 was heated by the glass softening heaters 14 to 700°C. where the glass has a viscosity of 10⁶ poises and softened.

[0129] Then, the GC vacuum pad 15, which had been kept waiting at theposition outside the glass softening heaters 14 and over the GC floatingmeans 10, was descended to the position of the preform 1 to catch thepreform by suction. At this point, the GC vacuum pad had been heated bythe radiation heat from the glass softening heaters 14 and had atemperature of from 300 to 400° C. and therefore it was not likely toreact with the low viscosity glass.

[0130] Then, the GC vacuum pad 15 holding the preform 1 was immediatelymoved to a position above the lower mold 34 as shown in FIG. 6 anddescended to a position near the molding surface 40 of the lower mold 34and the suction was stopped to place the preform 1 on the moldingsurface 40 of the lower mold 34. After that, the GC vacuum pad 15 wasremoved from the position above the lower mold 34 and returned to theoriginal waiting position and therefore there were no obstacles abovethe lower mold 34. The lower mold 34 was lifted up by the mold support38 in a moment to a position under the upper mold 35, which was disposedcoaxially with the lower mold 34 thereabove and fixed together with themold support 38, to press mold the preform for 10 seconds at a pressureof 100 kg/cm² in the mold assembly 39 comprising the upper mold 35, thelower mold 34 and the guide mold 36 guiding them so that a desiredthickness was obtained. Then, the mold heaters 44 were turned off andthe glass molded article 2 and the mold assembly 39 were allowed tocool. Seventy seconds later, when the temperatures of the upper mold 35and the lower mold 34 measured by the thermocouples 42 for measuringmold temperature became 534° C. corresponding to the glass transitionpoint, the glass molded article 2 was released and removed from the moldassembly 39.

[0131] With respect to the glass molded article 2 (outer diameter; φ 18mm, thickness; 2.9 mm, biconvex lens) obtained as described above, afterannealing, surface accuracy was evaluated by an interferometer andsurface quality was evaluated in terms of visual appearance and by astereoscopic microscope. Results are shown in Table 1. The evaluationwas performed with respect to five lenses obtained in the same manner(the same shall apply to the following examples). As a result, it wasfound that all of the lenses had good properties.

EXAMPLE 2

[0132] Though the glass floating and softening structure was changed,the same mold assembly and molding conditions as in Example 1 were used.

[0133] Inside of the closed chamber including the press moldingstructure and the glass heating structure was evacuated to vacuum and98% N₂+2% H₂ gas was introduced into the chamber to form an atmosphereof the gas in the chamber.

[0134] Then, the mold assembly was heated by the mold heaters 44 so thatthe upper mold 35 and the lower mold 34 had a temperature arounddeformation point of a preform 1 (the same glass type and the same shapeas in Example 1), i.e., 576° C., and maintained at the same temperature.On the other hand, as shown in FIG. 4, the glass preform 1 above aporous ceramic floating means 17 which was disposed on a floating meanssupport 19 and between the glass softening heaters 14 was heated to 700°C. where the glass has a viscosity of 10⁶ poises and softened, while itwas floated by N₂ gas fed from inside of the floating means support 19to lower part of the porous ceramic floating means 17 and blown off frompores of the floating means material at a flow rate of 200 ml/minute.

[0135] Then, a GC vacuum pad (not shown), which had been kept waiting ata position outside the glass softening heaters 14 and over the porousceramic floating means 17, was descended to catch the softened floatingpreform 1 by suction. Then, the GC vacuum pad holding the preform 1 wasimmediately moved to a position above the lower mold 34 as shown in FIG.6 and descended again to a position near the surface of the lower mold34 and the suction was stopped to place the preform 1 on the moldingsurface 40 of the lower mold 34. After that, the GC vacuum pad 15 wasmoved back to the original waiting position.

[0136] Then, the lower mold 34 was lifted up by the mold support 38 to aposition under the upper mold 35, which is disposed coaxially with thelower mold 34 thereabove, to press mold the glass material 1 for 10seconds at a pressure of 100 kg/cm² in the mold assembly 39 comprisingthe upper mold 35, the lower mold 34 and the guide mold 36 guiding themso that a desired thickness was obtained. Then, the mold heaters 44 wereturned off and, seventy seconds later, when the temperatures of theupper mold 35 and the lower mold 34 became 534° C. corresponding to theglass transition point, the glass molded article 2 was released andremoved from the mold assembly 39.

[0137] Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

EXAMPLE 3

[0138] Except that the glass floating and softening structure waschanged, Example 1 was repeated.

[0139] Inside of the closed chamber including the press moldingstructure and the glass heating structure was evacuated to vacuum and98% N₂+2% H₂ gas was introduced into the chamber to form an atmosphereof the gas in the chamber.

[0140] Then, the mold assembly was heated so that the upper mold 35 andthe lower mold 34 had a temperature around deformation point of apreform 1 (the same glass type and the same shape as in Example 1),i.e., 576° C. and maintained at that temperature.

[0141] On the other hand, the glass preform 1 was heated to 504° C. on aglass holding means 20 placed on a glass holding means support 21between glass preheating heaters 22 so that the preform had atemperature lower than its glass transition point by 30° C. andmaintained at that temperature. At that time, since the preform 1 doesnot exhibit flowability at the temperature, it does not need to befloated over the glass holding means 20.

[0142] Then, the GC vacuum pad, which had been kept waiting at theposition outside the glass preheating heaters 22 and over the glassholding means 20, was descended to catch the preform 1 by suction andmoved to a position above the tungsten alloy floating means 10, whichhad been preliminarily heated at 335° C. by the glass softening heater14 so that it had a temperature lower than the glass transitiontemperature by 200° C. Then the pad was descended and simultaneously thesuction was stopped to place the preform 1 on the receiving part of thefloating means 10. The GC vacuum pad 15 was kept waiting at a positionover the glass softening heaters 14.

[0143] The glass preform 1 was floated above the floating means 10 by ablow of 98% N₂+2% H₂ gas at a flow rate of 200 ml/minute, which was fedfrom inside of the floating means support 13 to the tungsten alloyfloating means 10, and heated rapidly by the glass softening heaters 14to 700° C. where the glass has a viscosity of 10⁶ poises. During thisoperation, because the temperature of the tungsten alloy floating means10 had been made lower than that of the glass preform 1 by 170° C. whenthe preform 1 was placed on the floating means, the temperature of thetungsten alloy floating means 10 was always lower than the temperatureof the glass even after the rapid heating. Therefore, the tungsten alloyfloating means 10 did not react with the glass.

[0144] Then, the GC vacuum pad 15, which had been kept waiting over theglass softening heaters 14, was descended to catch the floating softenedpreform 1 by suction and immediately moved to the position above thelower mold 34 and descended again to a position near the surface of thelower mold 34 and the suction was stopped to place the preform 1 on themolding surface 40 of the lower mold 34. After that, the GC vacuum pad15 was moved back to the original waiting position.

[0145] The lower mold 34 was lifted up by the mold support 38 to aposition under the upper mold 35 disposed coaxially with the lower mold34 thereabove to press mold the preform 1 for 10 seconds at a pressureof 100 kg/cm² in the mold assembly 39 shown FIG. 1 comprising the uppermold 35, the lower mold 34 and the guide mold 36 guiding them so that adesired thickness was obtained. Then, the mold heaters 44 were turnedoff and, seventy seconds later, when the temperatures of the upper mold35 and the lower mold 34 became 534° C. corresponding to the glasstransition point, the glass molded article 2 was released and removedfrom the mold assembly 39.

[0146] Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

EXAMPLE 4

[0147] Except that the mechanism for inserting a floating softened glassinto the mold assembly was changed, Example 1 was repeated.

[0148] Inside of the closed chamber including the press moldingstructure and the glass heating structure was evacuated to vacuum and98% N₂+2% H₂ gas was introduced into the chamber to form an atmosphereof the gas in the chamber.

[0149] Then, the mold assembly was heated so that the upper mold 35 andthe lower mold 34 had a temperature around deformation point of apreform 1 (the same glass type and the same shape as in Example 1),i.e., 576° C. and maintained at the same temperature. Then, as shown inFIG. 7, the glass preform 1 was floated over the GC floating means 10set on the floating means support 13 by a gas blow of 98% N₂+2% H₂ gasat a flow rate of 300 ml/minute, which was fed from inside of thefloating means support 13 to lower part of the GC floating means 10, andheated to 700° C. where the glass has a viscosity of 10⁶ poises while itwas floating. Then the floating means support 13 was moved to a positionsuch that the floating softened preform 1 was located just below theupper mold 35.

[0150] Then, as shown in FIG. 8, the floating means support 13 waslifted up to transfer the preform 1 to a position near the surface ofthe upper mold 35 and the preform 1 was contacted to the surface of theupper mold 35 by sucking from the suction holes 45 provided on theinside wall of the guide mold 36 for guiding the upper mold 35 and thelower mold 34 at positions corresponding to the side faces of thepreform 1. While sucking, the flow rate of the gas blow from thefloating means 10 may be temporarily increased to lift up the preform 1so that the preform can be more smoothly contacted to the surface of theupper mold 35.

[0151] Then, the floating means support 13 was moved from the positionbelow the upper mold 35 back to the initial position for heating andsoftening the glass. Simultaneously, as shown in FIG. 9, the lower mold34 was lifted up by the mold support 38 to a position under the uppermold 35 to press mold the preform 1 for 10 seconds at a pressure of 100kg/cm² in the mold assembly 39 comprising the upper mold 35, the lowermold 34 and the guide mold 36 guiding them so that a desired thicknesswas obtained. Then, the mold heaters 44 were turned off and, seventyseconds later, when the temperatures of the upper mold 35 and the lowermold 34 became 534° C. corresponding to the glass transition point, theglass molded article 2 was released and removed from the mold assembly39.

[0152] Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

EXAMPLE 5

[0153] Schematic views of the apparatus and the mold assembly used inthis example are shown in FIGS. 10, 11 and 18. The molds for molding hadthe same structure as in Example 1.

[0154] The closed chamber including the press molding structure and theglass heating structure was evacuated to vacuum and 98% N₂+2% H₂ gas wasintroduced into the chamber to form an atmosphere of the gas in thechamber.

[0155] Then, the mold assembly was heated by the mold heaters 44 untilthe temperatures of the upper mold 35 and the lower mold 34 reached to592° C. at which a glass preform 1 (marble-shaped hot molded articlehaving a surface-defect-free mirror surface, weight; 1800 mg, transitionpoint; 534° C., deformation point; 576° C.) had a viscosity of 101%poises and maintained at the same temperature.

[0156] On the other hand, as shown in FIG. 10, the preform 1 having adiameter slightly larger than that of the floating means on the GCfloating means 10 was floated by a gas blow of 98% N₂+2% H₂ gas at aflow rate of 600 ml/minute, which was fed from inside of the floatingmeans support 13 to lower part of the GC floating means 10, and heatedto 660° C. at which the glass had a viscosity of 10^(7.2) poises whileit was floating.

[0157] Then, a GC vacuum pad 24, which had been kept waiting at theposition outside the glass softening heaters 14 and over the GC floatingmeans 10, was descended to catch by suction a ring-like member 23disposed at the vicinity of the GC floating means 10 and immediatelyascended again. In this operation, when the periphery of the preform 1having a diameter slightly larger than the outer diameter of the GCfloating means 10 was pushed up by the inner periphery of the ring-likemember 23 and the preform 1 was transferred with the ring-like member23, the preform did not deformed by itself to sag and drop from thering-like member 23, because the transfer was performed within a shortperiod of time.

[0158] Then, as shown in FIG. 11, the GC vacuum pad 24 holding bysuction the ring-like member 23 on which the preform 1 was placed wasimmediately moved to a position above the lower mold 34. After that, itwas descended again to a position near the lower mold 34 and the suctionwas stopped to place the preform 1 on the molding surface 40 of thelower mold 34 and the ring-like member 23 on the flange provided at aposition slightly lower than the molding surface, respectively. Then,the GC vacuum pad 24 was removed from the position above the lower mold34 and the lower mold was lifted up by the mold support 38 to a positionunder the upper mold 35 disposed coaxially with the lower mold 34thereabove to press mold the preform 1 for 10 seconds at a pressure of100 kg/cm² in the mold assembly 39 comprising the upper mold 35, thelower mold 34 and the guide mold 36 guiding them so that a desiredthickness was obtained. Then, the mold heaters 44 were turned off and,seventy seconds later, when the temperatures of the upper mold 35 andthe lower mold 34 became 534° C. corresponding to the glass transitionpoint, the glass molded article 2 was released and removed from the moldassembly 39.

[0159] Properties of the glass molded article 2 (φ 25 mm, φ 20 mm aftercentering, biconvex lens) obtained as described above, after annealing,were evaluated in the same manner as in Example 1. Results are shown inTable 1. TABLE 1 Mold temperature at the when a molded Glass temperatureFloating Gas beginning glass was released Example (° C.) Flow Rate ofmolding from molds Evaluation of Glass Molded Articles No. (Viscosity)(cc/min) (Viscosity) (Viscosity) Surface Accuracy Surface Quality 1 700100 576 534 ◯ ◯ (10⁸ poises) (10^(10.7) poises) (10^(18.4) poises) 2 700200 576 534 ◯ ◯ (10⁸ poises) (10^(10.7) poises) (10^(18.4) poises) 3 700200 576 534 ◯ ◯ (10⁸ poises) (10^(10.7) poises) (10^(18.4) poises) 4 700360 576 534 ◯ ◯ (10⁸ poises) (10^(10.7) poises) (10^(18.4) poises) 5 660600 590 534 ◯ ◯ (10^(7.2) poises) (10¹⁰ poises) (10^(18.4) poises)

EXAMPLE 6

[0160] Glass molded articles were manufactured in the same manner as inExample 1 except that kinds of preform (glass types and shapes),floating gas flow rates and mold release temperatures indicated in Table2 were used. Properties of the obtained glass molded articles wereevaluated in the same manner as in Example 1. Results are shown in Table2. All of the glass molded articles exhibited good properties. TABLE 2Glass Article Floating Gas Mold Temperature Mold Release TemperatureFlow Rate (° C.) Temperature (° C.) Evaluation of Glass Molded Articles(Viscosity) Shape (cc/min) (Viscosity) (Viscosity) Surface PrecisionSurface Condition 683 ° C. Hot Formed 300 576 ° C. 549 ° C. ◯ ◯(10^(8.5) poises) Article 600 (10^(10.7) poises) (10^(12.3) poises) ◯ ◯Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ #800 diamond) Polished200 ◯ ◯ Sphere 400 ◯ ◯ 700 ° C. Hot Formed 300 568 ° C. 534 ° C. ◯ ◯(10⁸ poises) Article 600 (10^(11.2) poises) (10^(18.4) poises) ◯ ◯Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800 diamond) Polished200 ◯ Sphere 400 ◯ 718 ° C. Hot Formed 300 557 ° C. 525 ° C. ◯ ◯(10^(6.5) poises) Article 600 (10^(11.7) poises) (10¹⁴ poises) ◯ ◯Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800 diamond) PPolished 200 ◯ ◯ Sphere 400 ◯ ◯

EXAMPLE 7

[0161] Mold Assembly for Press Molding

[0162] The same mold assembly as in Example 1 was used.

[0163] Floating Means

[0164] In a single closed chamber (not shown) including the mold heatingstructure described above, there were provided floating means 10 (10 a,10 b), guide means 50 (50 a, 50 b) shown in FIG. 12 and the glasssoftening heaters 13 for heating and softening glass materials. Thefloating means 10 was a split floating means composed of glassy carbon(hereinafter referred to “GC split floating means”) and the guide means50 was a split cylindrical guide composed of the same material(hereinafter referred to as “GC split cylindrical guide”). The glassmaterial 1 was floated by a gas blow of 98% N₂+2% H₂ gas at a flow rateof 200 to 600 ml/minute supplied from inside of the GC split floatingmeans.

[0165] Heating for Softening and Pressing Processes

[0166] The closed chamber including the press molding structure and theglass heating structure described above was evacuated to vacuum and 98%N₂+2% H₂ gas was introduced into the chamber to form an atmosphere ofthe same gas in the chamber.

[0167] Then, the mold assembly was heated by the mold heaters 44 shownin FIG. 19 until the temperatures of the upper mold 35 and the lowermold 34 reached to 576° C., 565° C. or 557° C. measured by thethermocouples 43 for measuring mold temperature so that they had atemperature around the deformation point of a glass preform 1 identicalto that of Example 1 and maintained at the same temperature (Table 3).In this operation, the upper mold and the lower mold were separatelyheated at different positions and assembled together as an integratedmold assembly as shown in FIG. 19 upon molding.

[0168] On the other hand, the glass material 1 (preform) above the GCsplit floating means 10 was heated by the glass softening heaters 13 to683° C., 700° C. or 718° C. where the glass has a viscosity of 10^(6.5)to 10^(5.5) poises and maintained at the same temperatures.

[0169] Then, the GC split floating means 10 holding the floating heatedand softened glass material 1 was immediately moved to the position justabove the lower mold 34 and, as shown in FIG. 13, the GC split floatingmeans 10 a and the GC split floating means 10 b were moved in horizontaldirection to right and left in a moment to make an opening and drop theglass material 1 onto the molding surface 40 of the lower mold 34. TheGC split cylindrical guide 50 having an inner diameter allowing anappropriate clearance against the maximum outer diameter of the glassmaterial 1 was provided just above the GC split floating means 10. Whenthe GC split floating means was opened and the glass material wasdropped, the GC split cylindrical guide 50 served as a guide whichminimize the setting deviation of the glass material 1 on the lower mold34.

[0170] After the glass was dropped, the GC split cylindrical guides 50 aand 50 b were horizontally moved in opposite directions, right and left,to make an opening. Therefore, there are no obstacles above the lowermold 34 and the mold support 38 lifted up the lower mold in a moment toa position under the upper mold 35, which was disposed coaxially withthe lower mold 34 thereabove and fixed together with the mold support38, to press mold the glass material 1 for 10 seconds at a pressure of100 kg/cm² in the mold assembly comprising the upper mold 35, the lowermold 34 and the guide mold 36 guiding them so that a desired thicknesswas obtained as shown in FIG. 19. Then, the mold heaters 44 were turnedoff and the glass molded article 2 and the mold assembly were allowed tocool. Seventy seconds later, when the temperatures of the upper mold 35and the lower mold 34 measured by the thermocouples 43 for measuringmold temperature became 549° C., 534° C. or 525° C., the glass moldedarticle 2 was released and removed from the mold assembly.

[0171] With respect to the glass molded articles 2 (outer diameter; φ 18mm, thickness; 2.9 mm, biconvex lens) obtained as described above, afterannealing, surface accuracy was evaluated by an interferometer andsurface quality was evaluated in terms of visual appearance and by astereoscopic microscope. Results are shown in Table 3.

[0172] In Table 3, shown are results of evaluation of glass moldedarticles obtained by varying temperature of the softened glass material1, shape of the glass material 1, gas flow rate from the GC splitfloating means, mold temperature and mold release temperature. As aresult, it was found that all of the molded articles (lenses) had goodproperties. TABLE 3 Glass Article Floating Gas Mold Temperature MoldRelease Temperature Flow Rate (° C.) Temperature (° C.) Evaluation ofGlass Molded Articles (Viscosity) Shape (cc/min) (Viscosity) (Viscosity)Surface Precision Surface Condition 683 ° C. Hot Formed 300 576 ° C. 549° C. ◯ ◯ (10^(8.5) poises) Article 600 (10^(10.7) poises) (10^(12.3)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ #800diamond) Polished 200 ◯ ◯ Sphere 400 ◯ ◯ 700 ° C. Hot Formed 300 568 °C. 534 ° C. ◯ ◯ (10⁸ poises) Article 600 (10^(11.2) poises) (10^(18.4)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) Polished 200 ◯ Sphere 400 ◯ 718 ° C. Hot Formed 300 557 ° C.525 ° C. ◯ ◯ (10^(6.5) poises) Article 600 (10^(11.7) poises) (10¹⁴poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) P Polished 200 ◯ ◯ Sphere 400 ◯ ◯

EXAMPLES 8-1 TO 8-5

[0173] Mold Assembly for Press Molding

[0174] A mold assembly shown in FIG. 16 provided with the same molds asin Example 1 was used.

[0175] Floating Means and Transfer Means

[0176] In a single closed chamber (not shown) including the mold heatingstructure described above, there were also provided the floating meansand the transfer means shown in FIG. 2.

[0177] Glass softening heaters 14 for heating and softening glassmaterials (preform) 1 were also provided and a glassy carbon floatingmeans 10 (hereinafter referred to “GC floating means”) set on a floatingmeans support 13 was provided between the glass softening heaters 14.The glass material 1 was floated by a gas blow of 98% N₂+2% H₂ gas(Examples 8-1 to 8-3) or N₂ gas (Examples 8-4 and 8-5) at a flow rateindicated in Table 4 fed from inside of the floating means support 13 tolower part of the GC floating means 10.

[0178] Further, outside the glass softening heaters 14, there was aglassy carbon vacuum pad 15 (hereinafter referred to as “GC vacuumpad”), which can move vertically and horizontally, and it was normallywaiting at a position over the GC floating means 10.

[0179] Heating for Softening and Pressing Processes

[0180] The closed chamber (not shown) including the press moldingstructure and the glass heating structure described above was evacuatedto vacuum and 98% N₂+2% H₂ gas was introduced into the chamber to forman atmosphere of the same gas in the chamber.

[0181] The process will be exemplified below by utilizing a preform 1composed of barium borosilicate optical glass (marble-shaped hot formedarticle having a surface-defect-free mirror surface, weight; 1000 mg,transition point; 534° C., deformation point; 576° C.). The moldassembly was heated by the mold heaters 44 until the temperatures of theupper mold 35 and the lower mold 34 (mold temperature) measured by thethermocouples 43 for measuring mold temperature had reached to atemperature indicated in Table 4 at which the preform had a viscosityalso indicated in Table 4 and maintained at the same temperature. A partof relation between glass viscosity and its temperature was shown below.Glass Viscosity Temperature 10⁹ poises 614° C. 10¹⁰ poises 592° C. 10¹¹poises 572° C. 10¹² poises 554° C. 10^(12.7) poises 543° C. 10^(13.4)poises 534° C. 10^(14.5) poises 518° C.

[0182] On the other hand, the glass preform 1 above the GC floatingmeans 10 was heated by the glass softening heaters 14 to a temperatureindicated in Table 4 corresponding to a viscosity also indicated inTable 4 to soften it while it was floated. Further relation betweenglass viscosity and its temperature was shown below. Glass ViscosityTemperature 10^(5.5) poises 718° C. 10^(6.4) poises 686° C. 10^(7.3)poises 658° C. 10^(8.2) poises 634° C. 10^(8.8) poises 619° C.

[0183] Then, the GC vacuum pad 15, which had been kept waiting at aposition outside the glass softening heaters 14 and over the GC floatingmeans 10, was descended to the position of the preform 1 to catch thepreform 1 by suction. At this point, the GC vacuum pad had been heatedby the radiation heat from the glass softening heaters 14 and had atemperature of 300 to 400° C. and therefore it did not react with thelow viscosity glass.

[0184] Then, as shown in FIG. 6, the GC vacuum pad 15 holding thepreform 1 was immediately moved to the position above the lower mold 34and descended again to a position near the molding surface 40 of thelower mold 34 and the suction was stopped to place the preform 1 on themolding surface 40 of the lower mold 34. After that, the GC vacuum pad15 was moved from the position above the lower mold 34 back to theoriginal waiting position and therefore there are no obstacles above thelower mold 34. The mold support 38 lifted up the lower mold in a momentto a position under the upper mold 35, which was disposed coaxially withthe lower mold 34 thereabove and fixed together with the mold support38, to press mold the preform 1 for 10 seconds at a pressure of 100kg/cm² in the mold assembly 39 comprising the upper mold 35, the lowermold 34 and the guide mold 36 guiding them. In this molding process, thelower end of the guide mold 36 was stopped by a flange of the lower mold34 to give a thickness of the molded article larger than that of finalproduct by 30 μm. On the other hand, five seconds after the start of thepressing with the first cylinder, a pressure of 20 kg/cm² (Examples 8-1to 8-5) was applied to the back side of the upper mold 35 by a pushingbar 45 connected to the second cylinder which was provided inside thefirst cylinder to pressurize and hold the glass molded article 2 and themold assembly 39. Then, the mold heaters 44 were turned off and theglass molded article 2 and the mold assembly 39 were allowed to cool.After a period of time indicated in Table 4 as molding time (initialpress time [10 seconds]+secondary press time) was passed, moldtemperatures of the upper mold 35 and the lower mold 34 measured by thethermocouples 42 for measuring mold temperature reached to a temperatureindicated in Table 4 as mold release temperature and a desired thicknessof the glass molded article was obtained, the glass molded article 2 wasreleased and removed from the mold assembly 39. Relation between glassviscosity and its temperature was shown above.

[0185] With respect to the glass molded articles 2 (biconvex lenseshaving an outer diameter;φ 18 mm, thickness; 2.9 mm, and edge thickness;1.0 mm) obtained as described above, after annealing, surface accuracywas evaluated by an interferometer and surface quality was evaluated interms of visual appearance and by a stereoscopic microscope. Results areshown in Table 4 as Examples 8-1 to 8-5. As a result, it was found thatall of the lenses had good properties.

EXAMPLES 9-1 TO 9-5

[0186] Mold Assembly for Press Molding

[0187] The used mold assembly for press molding was the same as inExample 7 except that it did not have the pushing bar 45.

[0188] Floating Means

[0189] In a single closed chamber (not shown) including the mold heatingstructure described above, there were provided the floating means 10 (10a, 10 b), the guide means 50 (50 a, 50 b) shown in FIG. 12 and the glasssoftening heaters (not shown). The floating means 10 was a splitfloating means composed of glassy carbon (hereinafter referred to “GCsplit floating means”) and the guide means 50 was a split cylindricalguide composed of the same material (hereinafter referred to as “GCsplit cylindrical guide”). The glass material 1 was floated by a gasblow of 98% N₂+2% H₂ gas at a flow rate indicated in Table 4 suppliedfrom inside of the GC split floating means.

[0190] Heating for Softening and Pressing Processes

[0191] The closed chamber including the press molding structure and theglass heating structure described above was evacuated to vacuum and 98%N₂+2% H₂ gas was introduced into the chamber to form an atmosphere ofthe same gas in the chamber.

[0192] Then, the mold assembly was heated by the mold heaters 44 shownin FIG. 19 until the temperatures of the upper mold 35 and the lowermold 34 reached to 572° C. (Examples 9-1 to 9-3 and 9-5) or 554° C.(Example 9-4) measured by the thermocouples 43 for measuring moldtemperature at which temperatures the same glass material as in Example8 shows a viscosity of 10¹¹ or 10¹² poises, respectively, and maintainedat the same temperature. In this operation, the upper mold and the lowermold were separately heated at different positions and assembledtogether as an integrated mold assembly as shown in FIG. 19 uponmolding.

[0193] On the other hand, the glass material 1 above the GC splitfloating means 10 was heated by the glass softening heaters to 718° C.where the glass had a viscosity of 10^(5.5) poises as indicated in Table4 and maintained at the same temperature.

[0194] Then, the GC split floating means 10 holding the floating glassmaterial 1 was immediately moved to a position just above the lower mold34 and, as shown in FIG. 13, the GC split floating means 10 a and the GCsplit floating means 10 b were splitted and moved horizontally inopposite directions, right and left, in a moment to make an opening andthereby drop the glass material 1 onto the molding surface 40 of thelower mold 34. The GC split cylindrical guide 50 having an innerdiameter allowing an appropriate clearance against the maximum outerdiameter of the glass material 1 was provided just above the GC splitfloating means 10. When the GC split floating means 10 was opened andthe glass material 1 was dropped, the GC split cylindrical guide 50served as a guide which minimizes the setting deviation of the glassmaterial 1 on the lower mold 34.

[0195] After the glass was dropped, the GC split cylindrical guides 50 aand 50 b were horizontally moved in opposite directions, right and left,to make an opening. Therefore, there are no obstacles above the lowermold 34 and the mold support 38 lifted up the lower mold 34 in a momentto the upper mold 35, which was disposed coaxially with the lower mold34 thereabove and fixed together with the mold support 38, to press moldthe glass material 1 for 10 seconds at a pressure of 100 kg/cm² in themold assembly comprising the upper mold 35, the lower mold 34 and theguide mold 36 guiding them so that a desired thickness was obtained andthe pressure was changed to 50 kg/cm² in a moment. Then, the moldheaters 44 were turned off and the glass molded article 2 and the moldassembly were allowed to cool. After a period of time indicated in Table4 as molding time (initial press time [10 seconds]+secondary press time)was passed and the temperatures of the upper mold 35 and the lower mold34 measured by the thermocouples 43 for measuring mold temperaturereached to a temperature indicated in Table 4 as mold releasetemperature, the glass molded article 2 was released and removed fromthe mold assembly With respect to the glass molded articles 2 (biconvexlenses having an outer diameter; φ 18 mm, thickness; 2.9 mm and edgethickness; 1.0 mm) obtained as described above, after annealing, surfaceaccuracy was evaluated by an interferometer and surface quality wasevaluated in terms of visual appearance and by a stereoscopicmicroscope. Results are shown in Table 4.

[0196] In Table 4, shown are results of evaluation of glass moldedarticles obtained by varying temperature of the softened glass material1, shape of the glass material 1, gas flow rate from the GC splitfloating means, mold temperature and mold release temperature. As aresult, it was found that all of the molded articles (lenses) had goodproperties.

EXAMPLES 10-1 To 10-3

[0197] Glass molded articles (biconvex lenses having an outer diameter;φ18 mm, thickness; 2.9 mm and edge thickness; 1.0 mm) were obtained inthe same manner as in Example 8-1 except that the initial press time was5 seconds (Example 10-1), 30 seconds (Example 10-2) or 55 seconds(Example 10-3). With respect to the glass molded articles afterannealing, surface accuracy was evaluated by an interferometer andsurface quality was evaluated in terms of visual appearance and by astereoscopic microscope. Results are shown in Table 4.

Examples 11-1 and 11-2

[0198] Glass molded articles (biconvex lenses having an outer diameter;φ 18 mm, thickness; 2.9 mm and edge thickness; 1.0 mm) were obtained inthe same manner as in Example 8-1 except that the mold assembly wasallowed to start to cool at the start of the initial press (pressed witha pressure of 100 kg/cm²) (Example 11-1) or five second after the startof the initial press (Example 11-2). With respect to the glass moldedarticles after annealing, surface accuracy was evaluated by aninterferometer and surface quality was evaluated in terms of visualappearance and by a stereoscopic microscope. Results are shown in Table4. TABLE 4 Floating Mold Temper- Cool- Glass Gas ature at Start MoldingPressure Mold- ing Mold Temperature Evaluation of Exam- Temperature Flowof Molding (kg/cm²) ing Rate at Mold Release Glass Molded Articles ple(° C.) Rate (° C.) Initial Secondary Time (° C./ (° C.) Surface SurfaceNo. (Viscosity) (1/min) (Viscosity) Press Press (sec) min) (Viscosity)Precision Condition  8-1 686 ° C. 0.5 592 ° C. 100 20 85 47 534 ° C. ⊚ ⊚(10^(8.4) poises) (10¹⁰ poises) (10^(18.4) poises)  8-2 686 ° C. 0.5 572° C. 100 20 70 26 566 ° C. ⊚ ⊚ (10^(8.4) poises) (10¹¹ poises)(10^(12.5) poises)  8-3 658 ° C. 1.0 614 ° C. 100 20 85 65 534 ° C. ⊚ ⊚(10^(7.3) poises) (10⁹ poises) (10^(13.4) poises)  8-4 658 ° C. 1.0 592° C. 100 20 50 57 554 ° C. ◯ ⊚ (10^(7.3) poises) (10¹⁰ poises)(l0^(12.0) poises)  8-5 620 ° C. 1.0 610 ° C. 100 20 90 64 525 ° C. ⊚ ⊚(10^(8.8) poises) (10^(9.2) poises) (10^(14. 0) poises)  9-1 718 ° C.0.5 572 ° C. 100 50 70 29 563 ° C. ⊚ ⊚ (10^(5.5) poises) (10¹¹ poises)(10^(12.7) poises)  9-2 718 ° C. 0.5 572 ° C. 100 50 70 43 529 ° C. ⊚ ⊚(10^(5.5) poises) (10¹¹ poises) (10^(13.7) poises)  9-3 718 ° C. 0.5 572° C. 100 50 85 45 516 ° C. ◯ ⊚ (10^(5.5) poises) (10¹¹ poises)(10^(14.7) poises)  9-4 718 ° C. 0.5 554 ° C. 100 50 70 21 534 ° C. ⊚ ⊚(10^(5.5) poises) (10¹² poises) (10^(13.4 poises))  9-5 718 ° C. 0.5 572° C. 100 20 82 45 518 ° C. ⊚ ⊚ (10^(5.5) poises) (10¹¹ poises)(10^(14.5) poises) 10-1 686 ° C. 0.5 592 ° C. 100 20 80 47 534 ° C. ⊚ ⊚(10^(8.4) poises) (10¹⁰ poises) (10^(18.4) poises) 10-2 686 ° C. 0.5 592° C. 100 20 105 47 534 ° C. ⊚ ⊚ (10^(8.4) poises) (10¹⁰ poises)(10^(18.4) poises) 10-3 686 ° C. 0.5 592 ° C. 100 20 130 47 534 ° C. ⊚ ⊚(10^(8.4) poises) (1010 poises) (10^(18.4) poises) ⊚ ⊚ 11-1 686 ° C. 0.5592 ° C. 100 20 75 47 534 ° C. ⊚ ⊚ (10^(8.4) poises) (10¹⁰ poises)(10^(18.4) poises) 11-2 686 ° C. 0.5 592 ° C. 100 20 80 47 534 ° C. ⊚ ⊚(10^(8.4) poises) (10¹⁰ poises) (10^(18.4) poises)

[0199] The symbols used in the evaluation of the glass molded articleshave the following meanings.

[0200] Surface Accuracy

[0201] ∘: not more than 0.5 fringes of irregularity

[0202] ⊚: not more than 0.2 fringes of irregularity

[0203] Surface Quality

[0204] ⊚: good

[0205] In the above examples of the present invention, used were themolds obtained by forming a silicon carbide layer on a silicon carbidesintered body by a CVD technique and forming thereon an i-carbon layerby an ion-plating technique. However, in addition to such molds, it wasfound that those composed of silicon, silicon nitride, tungsten carbideor cermets of aluminum oxide-base and cermets of titanium carbide-baseand such materials further coated with diamond, heat resistant metals,noble metal alloys, ceramics of carbides, nitrides, borides, oxides andthe like may be used. However, the i-carbon layer was particularlypreferred since it showed good mold release property.

[0206] In the above Examples 8 to 11, the cycle time was a sum ofmolding time and recovery time of mold temperature (time required forelevating a mold temperature at mold release to a temperature requiredfor starting the molding). Since the molds were heated by resistanceheating in those examples, the recovery time was about 35 seconds.Therefore, the cycle time was about 85 to 165 seconds.

[0207] The recovery time may be shortened to about 10 seconds byperforming the heating of the molds with high-frequency heating orinfrared heating, and hence the cycle time may be shortened as much asthe time shortened by the heating means.

What is claimed is:
 1. A process for manufacturing glass opticalelements by press molding a heated and softened glass material inpreheated molds wherein the glass material is heated while the materialis floated by a gas blow and the heated and softened glass material istransferred to the preheated molds and then press molded.
 2. A processaccording to claim 1 wherein the glass material is a glass preform.
 3. Aprocess according to claim 2 wherein the glass preform is floated by agas blow which is blown off upward from an upper opening.
 4. A processaccording to claim 3 wherein the upper opening has a diameter smallerthan, equal to or bigger than a diameter of the preform.
 5. A processaccording to claim 3 wherein the gas blow is blown off from at least oneopening on the bottom of the upper opening.
 6. A process according toclaim 2 wherein the glass preform is floated by a gas blow which isblown off from a porous material which has a spherical surface having acurvature similar to that of the preform or a flat surface.
 7. A processaccording to claim 2 wherein the glass preform having a temperature offrom room temperature to 200° C. is heated while it is floated by a gasblow.
 8. A process according to claim 2 wherein the glass preform isheated to a temperature lower than its glass transition temperature by30° C. or more and then it is further heated and softened while it isfloated by a gas blow.
 9. A process according to claim 2 wherein theheated and softened glass preform has a viscosity of from 10^(5.5) to10^(9.0) poises.
 10. A process according to claim 2 wherein the heatedand softened glass preform is held by suction and transferred to thepreheated molds.
 11. A process according to claim 10 wherein the heatedand softened glass preform is held by suction and transferred to themolds by means of a movable suction holding means having a loweropening.
 12. A process according to claim 11 wherein the softened glasspreform is held by suction and transferred to the molds by means of amovable suction holding means having a lower opening and then thesoftened preform is press molded between molding surfaces of a lowermold and an upper mold.
 13. A process according to claim 2 wherein theheated and softened glass preform is held by sucking from suction holesprovided in the vicinity of the molding surface of the upper mold.
 14. Aprocess according to claim 13 wherein the lower mold is moved to aposition under the softened preform held by suction at the vicinity ofthe molding surface of the upper mold, or the softened preform held bysuction at the vicinity of the molding surface of the upper mold ismoved to a position above the molding surface of the lower mold and thenthe softened preform is press molded between molding surfaces of thelower mold and the upper mold.
 15. A process according to claim 2wherein the heated and softened preform is placed on a ring-like memberhaving an inner diameter smaller than an outer diameter of the preformand transferred to the preheated molds together with the ring-likemember.
 16. A process according to claim 15 wherein the preform isfloated by a gas blow which is blown off upward from an upper opening.17. A process according to claim 16 wherein the upper opening has adiameter smaller than, equal to or bigger than a diameter of thepreform.
 18. A process according to claim 17 wherein the upper openinghas an outer diameter smaller than the inner diameter of the ring-likemember.
 19. A process according to claim 1 for manufacturing glassoptical elements by press molding a heated and softened a glass gob inpreheated molds wherein the heated and softened glass gob is transferredto the preheated molds by holding it by suction or placing it on aring-like member having an inner diameter smaller than the outerdiameter of the glass gob and subjected to press molding.
 20. A processaccording to claim 19 wherein the glass gob is held by suction by meansof a movable suction holding means having a lower opening or held bysucking from suction holes provided in the vicinity of the moldingsurface of the upper mold.
 21. A process according to claim 1 whereinthe heated and softened glass material is transferred to the preheatedmolds by dropping the material.
 22. A process according to claim 21wherein the glass material is a glass preform.
 23. A process accordingto claim 22 wherein the heated and softened glass preform is dropped bysplitting a floating means used for heating the preform into two or morepieces and removing the pieces.
 24. A process according to claim 21 formanufacturing glass optical elements by press molding a heated andsoftened glass gob in preheated molds wherein the glass gob is softenedby heating while it is floated by a gas blow and the heated and softenedglass gob is dropped by splitting a floating means used for heating theglass gob into two or more pieces and removing the pieces so that theglass gob is transferred to the preheated molds and subjected to pressmolding.
 25. A process according to claim 24 wherein the heated andsoftened glass gob has a viscosity of from 10^(5.5) to 10^(9.0) poises.26. A process according to claim 21 wherein a guide means is used fordropping the heated and softened glass preform or glass gob in a certaindirection.
 27. A process for manufacturing glass optical elements bypress molding a preheated and softened glass material in preheatedmolds, which comprises: heating a glass material at a temperature atwhich the glass material has a viscosity of lower than 10⁹ poises,preheating molds at a temperature at which the glass material has aviscosity of from 10⁹ to 10¹² poises, subjecting the heated and softenedglass material to initial press in the preheated molds for 3 to 60seconds, starting to cool the vicinity of molding surface of the moldsat a rate of 20° C./minute or higher upon starting of, or during, orafter the initial press, and removing a molded glass article from themolds after the temperature of the vicinity of the molding surface ofthe mold becomes a temperature equal to or lower than a temperature atwhich the glass material has a viscosity of 10¹² poises.
 28. A processaccording to claim 27 wherein the molding surfaces of the molds have anamorphous and/or crystalline carbon mono-component or mixture layer ofgraphite structure and/or diamond structure.
 29. A process according toclaim 27 wherein, after the initial press, secondary press is carriedout at a pressure corresponding to 5 to 70% of the pressure of theinitial press and the vicinity of the molding surface is cooled whilethe pressure of the secondary press is maintained.
 30. A processaccording to claim 29 wherein the heated and softened glass material issubjected to the initial press so that the material has a thicknesswithin a range of from a thickness smaller than that of final productsby 0.03 mm to a thickness larger than the same by 0.15 mm, and thensubjected to the secondary press.
 31. A process according to claim 30wherein the initial press of the heated and softened glass material isstopped by a means for stopping initial press when the glass materialhas a desired center thickness, and the secondary press is startedbefore the initial press is stopped or upon the stop of the initialpress.
 32. A process according to claim 31 wherein the initial press andthe secondary press are performed by a double cylinder structure.
 33. Aprocess according to claim 27 wherein the mold release of the moldedglass articles is performed when the vicinity of the molding surface hasa temperature at which the glass material has a viscosity of from 10¹³to 10^(14.5) poises.
 34. A process according to claim 27 wherein theglass material is a glass preform or a glass gob.
 35. A processaccording to claim 27 wherein the glass material is heated while it isfloated by a gas blow.
 36. A process according to claim 35 wherein theheated and softened glass material is transferred to the preheated moldsby holding the glass material by suction or by dropping the glassmaterial.
 37. A process according to claim 36 wherein the heated andsoftened glass material is dropped by splitting a floating means usedfor heating the glass material into two or more pieces and removing thepieces.
 38. A process according to claim 37 wherein a guide means isused for dropping the heated and softened glass material in a certaindirection.